Magnetic retrieving tool



1956 G. w. J. TROWBRIDGE 2,72%494 MAGNETIC RETRIEVING TOOL 4 Sheets-Sheet 2 Filed Sept. 14, 1951 F/GZ.

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1956 ca. w. J. TROWBRlDGE 2,729,494

MAGNETIC RETRIEVING TOOL Filed Sept. 14, 1951 4 Sheets-Sheet 5 F/GSv nuentor g9 Attorney;

E G m R B W G R T 3km W G MAGNETIC RETRIEVING TOOL 4 Sheets-Sheet Filed. Sept. 1.4;, 1951 w J Inventor my By Y United States Patent MAGNETIC RETRIEVING TOOL George William Job Trowbridge, Surbiton, England, as-

signor to The Kingston Instrument Company Ltd., S urbiton, England, a British company Application September 14, 1951, Serial No. 246,693

Claims priority, application Great Britain September 28, 1950 9 Claims. (Cl. 294-655) This invention relates to magnet devices for recovering iron or similar articles from boreholes, wells or the like.

In such operations as oil-well drilling and mining, it is frequently necessary to extract broken parts of drilling tools or the like from a hole being drilled, to avoid unnecessary damage to a fresh drilling tool. As such tools are largely of steel, a magnet is a convenient device for extracting such broken parts and electromagnets have been used for this purpose. In order to avoid complications such as the provision of an electric power supply, permanent magnets have been proposed for such work. As however the broken parts or the like may be of considerable weight such magnets need to be of considerable power and it has unfortunately been found that in general magnet materials having the best magnetic characteristics tend to be brittle and insufficiently resistant to mechanical wear, with the result that frequent and costly replacements are necessary.

It is therefore an object of this invention to provide a magnet device for the purposes outlined, which whilst efficient in operation avoids or reduces the complications and expenses referred to above.

According to the invention, there is provided a magnetic retrieving tool for well bores, comprising at least one permanent magnet, a cap member of magnetic material, a body, and means detachably securing the magnet and body together, said cap member being mounted in a readily detachable manner on the body in contact with at least one pole of the magnet. The reason for employing a readily detachable cap member is as follows: Briefly, ma terials which are good for the manufacture of permanent magnets tend to have insufficient mechanical strength and do not stand up to the comparatively rough treatment received when used for fishing. Although the cap may be made of substantially stronger materials than the magnets, it is nevertheless liable to be considerably defaced and distorted during use and requires more or less frequent replacement. Such replacement can, when the cap member is made readily detachable from the body, be made with dispatch and without the necessity for replacing any undamaged parts which is needlessly expensive. The feature of readily detachability for the cap member is of further importance in that it becomes relatively simple to fit on cap members having special shapes required for particular fishing tasks.

Freferably the detachable cap member has portions of high permeability material adjacent the pole or poles, and

where, as is preferred, the magnet is of generally cylindrical shape, the cap may comprise a cylindrical sleeve, with a disc closing one of its ends. The cap member may also be of composite form including for instance an annular disc or two substantially semi-circular discs which are adapted to fit into the body and to rest on the end of the magnet. Various means may be employed to secure the cap to the magnet, such as cooperating screw threads, grub screws, locating pins or the like but we prefer to arrange that the cap forms a detachable end to the body, lugs projecting from the cap being bent to engage corresponding 2,729,494 Patented Jan. 3, 1956 recesses in an adjacent part of the body or of a member associated therewith. Locating pins or studs extending through the cap into the magnet may also be provided to prevent relative movement of the magnet and the cap.

A clear passage is formed through said magnet and cap for the passage of water, sludge or the like, as may be needed for example in oil wells. Normally the magnet is of a straight bar form but in many cases a horseshoe magnet is preferable either in a one-piece form or more conveniently as a built-up assembly, e. g. of two bar magnets and a bridge-piece.

In order that the invention may be well understood, various preferred embodiments thereof will now be described, with reference to the accompanying drawings, in which:

Figure l is a sectional side elevation of a magnet device embodying the invention,

Figure 2 is a sectional view of the device, the section being on line 11-11 of Fig. 1.

Figure 3 is an end view of Fig. 1.

Figure 4 is a view similar to Fig. l, of a modified form of device,

Figure 5 is an end view of Figure 4.

Figure 6 is a view similar to Figures 1 and 3 of a modified device.

Figure 7 is a view similar to Figures 1 and 3 of another modified device, and

Figure 8 is an end view of Figure 7.

In one preferred form of magnet device according to the invention, shown in Figs. 1 and 2, we provide a body 1 of bronze or other non-magnetic material in the form of a cylindrical tube, and inside the forward end of such tube are located two magnets 2, 2, each being of segmental section (Fig. 2) and being held in spaced relation by separator members 3 of non-magnetic material so that a square central passage 4 is left unobstructed. The said magnets 2, 2 extend approximately half-way along the body 1 and within said body and in contact with said magnets is a bridge-piece 5 comprising a cylindrical plug of high permeability magnetic material. A central bore 6 in said bridge-piece 5 provides a continuation of the central passage between the magnets. Rearwardly of the bridgepiece 5 the inside diameter of the body 1 is reduced to provide a central passage 7, which is tapped, and an annular shoulder 8 against which said bridge-piece abuts. The central portion of the rear face of said bridge-piece carries an integral threaded spigot 9 which is screwed into the pas sage 7. The bore 6 extends through said spigot and its rearward portion 10 is of square section. Beyond the spigot 9 the passage 7 extends to the rearward end of the body 1 and is tapped to receive a. cooperating threaded member (not shown) upon which the whole assembly may be supported e. g. by suspension.

It will be seen that a continuous path through the centre of the device is provided by the passage 4, bore 6 and passage 7. This serves, e. g. when the device is lowered into an oil-well, to allow sludge, mud or the like to be pumped out of such well, a suitable pump being connected to the rearward end of the device.

The forward end of the device is provided with a retaining bush 11 of non-magnetic material screwed into the body 1, and said bush and body cooperate to hold a retaining ring 12 of thick wire made of bronze or other non-magnetic material which rests in a circumferential groove in the assembly of magnets 2, 2 and separator members 3, thus said assembly and body are held in fixed relative positions.

A cap 13 covers the forward end of the magnet and separator assembly, said cap comprising a disc with a flange 14 carrying lugs 14a. The cap 13 is retained in contact with the magnet by means of the lugs 14a which are deformed towards the axis of the magnet to enter recesses on the bush 11. The cap 13 .is provided with portions 13a of high permeability material in register with the magnet poles and the remainder of said cap is of non-magnetic material. -Set-screws 15 extending through the :cap into the separators serve'toipreventrelative rotation between the cap, -and the magnets. The cap has .a central aperture continuing with the passage '4.

The magnets 2, 2 are disposed so that one presents a south pole at zits'forward :end, the other a north pole, thus in effect the assemblyof the 't-w'omagnets and the bridgepiece '5 constitutes a single horse-shoe magnet, this arrangement being found to give a more concentrated field at the forward end than with a singl'e'magnet, as will be described. Also, with this horseshoe arrangement :a keeper can readily be applied, when the device is out of use, yet it will be :noted that the composite magnet is in the form of a straight bar.

However, where simplicity of construction is more importantthan concentra'tion-oftfield, a single magnet device as shown in Figures 4 and may be used. Itwill beseen that the arrangement of the body .21 which :is bronze or other non-magnetic material and cap 22 is-similar to that of the body and cap in the two-magnet device described, but in this case the magnets 2, separators Sand bridgepiece 5 are replaced by a single magnet 23, this magnet having a central bore 24 (corresponding'to passage 4) in communication with a passage 25 in the body 21 and an aperture 26 in the cap 22. The cap 22 is here all of high permeability material, and the direction in which the magnet is arranged as regards polarity is of course immaterial.

In another form of device embodying the invention, a single magnet may be used, the body being made of magnetic material similar to that of the cap, and a suitable sleeve of non-magnetic material being interposed between said body and the magnet. Appropriate modification of the cap is then made so that the forward end of the device presents a central disc of'magnetic material in contact with the neighbouring end of the magnet and an-outer ring of such material magnetically connected'viathe body to the rearward pole of said magnet, so that two opposite magnetic poles are presentedtoany object to be picked up.

Such a further form of device according to the invention is shown in Fig. 6, and it will be seen that here the body 31, of magnetic material, extends to the forward end of the device, and the cap 32 is a disc seated on a tubular magnet formed of two sections 33a, 3312 within said body, a non-magnetic spacer 34 of material such as babbitt metal being included between the body 31 and the tubular magnet.

The body 31, cap 32 and magnet 33a, 33b, are held together by forming the inner surface of the body 31 with an undercut, i. e. a'taper such that the internal diameter remote from the cap is larger than at the cap end. The outer surface of the magnet 33a, 33b is alsotapered, at a somewhat greater angle, and thus the sleeve 34 is of wedge section and cooperates with said undercut to retain the magnet in place. Babbitt metal is preferred because it may readily be melted and poured in when assembling, while if at any time replacement of the magnet is undertaken, the babbitt can quite easily be extracted, e. g. by gentle heating.

A passage 35 is provided through the centre of the magnets and of the body, for the passage of mud sludge or the like as previously mentioned.

The embodiment of Figures 7 and 8 has an arrangement of magnets which with the body form a composite magnet of horse-shoe form, similar to the arrangement of Figs. 1 and 2. In this embodiment however, the body is made in two parts 41, 42 which are screwed together, providing a continuously cylindrical external surface.

The part 41 is a plain, thin cylindrical shell, while part 42 has, at its forward end, a practically solid part 42a through .which'only a small central hole 43 extends, while theirear-end 42b hasa central passage-44 larger "than hole 43 which is tapped and may receive suspension means, not shown, such as a cooperating threaded member, as previously mentioned.

In the shell 41 magnets 45 and separator members as of non-magnetic material e. g. bronze are assembled, the arrangement being generally similar to that of the members 3, 3 in Figs. 1 and 2. At the forward end, however, the separator members 46 extend so that their ends are flush with the end of the shell, while the ends of the magnets are slightly recessed, the generally D-shaped recesses thus provided being occupied by correspondingly shaped thin protector members 47, of magnetic material such as soft iron.

Thus in this embodiment, in effect a composite cap member is used, comprising the protector members 47, the ends of the separator members 46 and the end portion of the shell 41.

The magnets 45, separator members 46 and protector members 47 are retained in position partly by providing the last-named members with slightly bevelled edges, on to which the rim of the shell 41 is crimped or-clinched at a number of points, say ten, equally spaced around its circumference, as indicated at 48. Also, screws 49 extending through the shell 41 into tapped holes in the separator members 46, and dowel pins 50 resting in cooperating grooves of said separator members and of the magnets 45, serve to complete the rigidity of the assembly, and give the strength required if heavy loads are to be lifted. As in previous embodiments, a central passage extends from endtoend of the whole device.

The embodiment of Fig. 7 is particularly suited to situations where it is desired to use expensive materials for-the outer casee. g. stainless steel is often desirable. In such cases unnecessary expense may be avoided by using the expensive material such as stainless steel for the forward end, i. e. the shell 41, while the rear part 42 may be of cheaper-material such as mild steel.

It will be noted that in the forms of the device shown in Figs. 1, 2, 6 and 7, the magnet or magnets are each in twopieces, and it is of course possible for each magnet to be manufactured as a one-piecemember, or in more than two pieces. We'have found two-piece magnets to be convenient for most purposes, and then when larger or smaller devices are required, casings of appropriate sizes may be used in conjunction with an appropriate number of standard magnet pieces.

It will also be understood that, while the embodiments shown present plane forward end faces, normal to the axis of the device, other forms of end face may be provided. Thus plane end faces may be at any desired angle to said axis, or if desired convexly or concavely coned faces may be produced by suitable shaping of various components, and in fact end faces suitable to receive loads of any configuration may be employed without departure from the scope of the invention.

What we claim is:

1. A magnetic retrieving tool for well bores comprising at least one permanent magnet, a cap member of magnetic material, a body, means detachably securing said magnet and body together, and means detachably securingsaid cap member to the end of said body and in contact with at least one pole of said magnet thereby to facilitate replacement of said cap member.

'2. A magnetic retrieving tool for wellbores comprising at least one permanent magnet, a cap member of magnetic material, a body, means detachably securing said magnet and body together, and means detachably securing said cap member to the end of said body and in contact with at least one pole of said magnet thereby to facilitate replacement of-said cap member, said permanent magnet comprising two similar straight bar magnets, a bridge-piece'magnetically connecting said magnets and at least one separator member 'of non-magnetic material between'said bar magnets thus constituting a composite magnet of horseshoe form.

3. A magnetic retrieving tool for well bores comprising a permanent magnet, a cap member of magnetic material in contact with at least one pole of said magnet, a body member in the form of a sleeve, and a threaded ring, said cap member, said threaded ring and said sleeve all serving in cooperation to enclose said magnet, said cap member having a plurality of peripherally disposed lugs cooperating with complementary portions of said threaded ring, said threaded ring and said sleeve being threadedly secured together and embracing an annular upstanding rib on said magnet.

4. A magnetic retrieving tool for well bores as claimed in claim 3, in which said rib comprises a plain ring sunk in the surface of said magnet.

5. A magnetic retrieving tool for well bores compris ing a body having a portion of magnetic material, magnets magnetically connected together by the magnetic portion of said body to form a composite permanent magnet of horse-shoe form, two substantially D-shaped protector members of magnetic material, and two separator members of non-magnetic material disposed between said magnets, said body being formed as two parts detachably secured together of which one is a cylindrical shell enclosing the composite magnet, said composite magnet being recessed into said shell, said separators projecting beyond the lower ends of said magnets, and said protector members being accommodated between the projecting portions of said separator members and the end portion of the shell, means being provided to retain said shell, magnets, and separator members in assembled relation to each other so as to provide a readily detachable cap member for the composite magnet.

6. A magnetic retrieving tool for well bores comprising a body having a portion of magnetic material, magnets magnetically connected together by the magnetic portion of said body to form a composite permanent magnet of horse-shoe form, two substantially D-shaped protector members of magnetic material, and two separator members of non-magnetic material disposed between said magnets, said body being formed as two parts detachably secured together of which one is a cylindrical shell enclosing the composite magnet, said composite magnet being recessed into said shell, said separator members projecting beyond the lower ends of said magnets, and

said protector members being accommodated between the 5 projecting portions of said separator members and the end portion of the shell, screws being provided to secure said shell to said separator members and dowel pins being placed in cooperating grooves of the separator members and the magnets.

7. A magnetic retrieving tool for well bores comprising at least one tubular permanent magnet, an annular cap member of ferromagnetic material in contact with one pole of said magnet, and a sleeve, means detachably securing said cap member to said sleeve, said sleeve and cap member together serving to enclose said magnet.

8. A magnetic retrieving tool for well bores comprising a cylindrical body of magnetic material, having an axial bore therethrough, a pair of D-shaped permanent magnets arranged back-to-back and with their upper end faces in contact with the lower end face of said body to thereby form a composite permanent magnet of horseshoe form, a pair of separator members of non-magnetic material disposed between the back faces of said magnets, the inner ends of said separator members being spaced apart to establish an axial passageway forming a continuation of the axial bore through said body, and the lower end portions of said separators extending beyond the lower end faces of said magnets, D-shaped protector members of magnetic material individual to said magnets, said protector members conforming to the configuration of the lower end faces of said magnets and being in contact therewith, and a cylindrical shell of nonmagnetic material enclosing said magnets and having an upper threaded portion adapted to screw onto a threaded portion of said body, the lower end of said shell including portions extending radially inward to overlie and retain the peripheral portions of said protector members.

9. A magnetic retrieving tool for well bores as defined in claim 8 and which further includes retaining screws extending through said shell into said separator members, and dowel pins disposed in confronting grooves provided in the backs of said magnets and said separator members.

References Cited in the file of this patent UNITED STATES PATENTS 974,760 Eastwood Nov. 1, 1910 2,092,316 Lane Sept. 7, 1937 2,179,625 Groden Nov. 14, 1939 2,431,361 Athy Nov. 25, 1947 

